The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/imgact_shell.c

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    1 /*-
    2  * Copyright (c) 1993, David Greenman
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: releng/8.2/sys/kern/imgact_shell.c 199583 2009-11-20 15:27:52Z jhb $");
   29 
   30 #include <sys/param.h>
   31 #include <sys/vnode.h>
   32 #include <sys/proc.h>
   33 #include <sys/sbuf.h>
   34 #include <sys/systm.h>
   35 #include <sys/sysproto.h>
   36 #include <sys/exec.h>
   37 #include <sys/imgact.h>
   38 #include <sys/kernel.h>
   39 
   40 #if BYTE_ORDER == LITTLE_ENDIAN
   41 #define SHELLMAGIC      0x2123 /* #! */
   42 #else
   43 #define SHELLMAGIC      0x2321
   44 #endif
   45 
   46 /*
   47  * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE.  This is
   48  * significant because the caller has only mapped in one page of the
   49  * file we're reading.  This code should be changed to know how to
   50  * read in the second page, but I'm not doing that just yet...
   51  */
   52 #if MAXSHELLCMDLEN > PAGE_SIZE
   53 #error "MAXSHELLCMDLEN is larger than a single page!"
   54 #endif
   55 
   56 /**
   57  * Shell interpreter image activator. An interpreter name beginning at
   58  * imgp->args->begin_argv is the minimal successful exit requirement.
   59  *
   60  * If the given file is a shell-script, then the first line will start
   61  * with the two characters `#!' (aka SHELLMAGIC), followed by the name
   62  * of the shell-interpreter to run, followed by zero or more tokens.
   63  *
   64  * The interpreter is then started up such that it will see:
   65  *    arg[0] -> The name of interpreter as specified after `#!' in the
   66  *              first line of the script.  The interpreter name must
   67  *              not be longer than MAXSHELLCMDLEN bytes.
   68  *    arg[1] -> *If* there are any additional tokens on the first line,
   69  *              then we add a new arg[1], which is a copy of the rest of
   70  *              that line.  The copy starts at the first token after the
   71  *              interpreter name.  We leave it to the interpreter to
   72  *              parse the tokens in that value.
   73  *    arg[x] -> the full pathname of the script.  This will either be
   74  *              arg[2] or arg[1], depending on whether or not tokens
   75  *              were found after the interpreter name.
   76  *  arg[x+1] -> all the arguments that were specified on the original
   77  *              command line.
   78  *
   79  * This processing is described in the execve(2) man page.
   80  */
   81 
   82 /*
   83  * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
   84  * found on the first line of the script, and setup each token as a separate
   85  * value in arg[].  This extra processing did not match the behavior of other
   86  * OS's, and caused a few subtle problems.  For one, it meant the kernel was
   87  * deciding how those values should be parsed (wrt characters for quoting or
   88  * comments, etc), while the interpreter might have other rules for parsing.
   89  * It also meant the interpreter had no way of knowing which arguments came
   90  * from the first line of the shell script, and which arguments were specified
   91  * by the user on the command line.  That extra processing was dropped in the
   92  * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
   93  */
   94 int
   95 exec_shell_imgact(imgp)
   96         struct image_params *imgp;
   97 {
   98         const char *image_header = imgp->image_header;
   99         const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
  100         int error, offset;
  101         size_t length, clength;
  102         struct vattr vattr;
  103         struct sbuf *sname;
  104 
  105         /* a shell script? */
  106         if (((const short *) image_header)[0] != SHELLMAGIC)
  107                 return(-1);
  108 
  109         /*
  110          * Don't allow a shell script to be the shell for a shell
  111          *      script. :-)
  112          */
  113         if (imgp->interpreted)
  114                 return(ENOEXEC);
  115 
  116         imgp->interpreted = 1;
  117 
  118         /*
  119          * At this point we have the first page of the file mapped.
  120          * However, we don't know how far into the page the contents are
  121          * valid -- the actual file might be much shorter than the page.
  122          * So find out the file size.
  123          */
  124         error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
  125         if (error)
  126                 return (error);
  127 
  128         /*
  129          * Copy shell name and arguments from image_header into a string
  130          *      buffer.  Remember that the caller has mapped only the
  131          *      first page of the file into memory.
  132          */
  133         clength = (vattr.va_size > PAGE_SIZE) ? PAGE_SIZE : vattr.va_size;
  134 
  135         maxp = &image_header[clength];
  136         ihp = &image_header[2];
  137 
  138         /*
  139          * Find the beginning and end of the interpreter_name.  If the
  140          * line does not include any interpreter, or if the name which
  141          * was found is too long, we bail out.
  142          */
  143         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  144                 ihp++;
  145         interpb = ihp;
  146         while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
  147             && (*ihp != '\0')))
  148                 ihp++;
  149         interpe = ihp;
  150         if (interpb == interpe)
  151                 return (ENOEXEC);
  152         if ((interpe - interpb) >= MAXSHELLCMDLEN)
  153                 return (ENAMETOOLONG);
  154 
  155         /*
  156          * Find the beginning of the options (if any), and the end-of-line.
  157          * Then trim the trailing blanks off the value.  Note that some
  158          * other operating systems do *not* trim the trailing whitespace...
  159          */
  160         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  161                 ihp++;
  162         optb = ihp;
  163         while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
  164                 ihp++;
  165         opte = ihp;
  166         while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
  167                 opte = ihp;
  168 
  169         if (imgp->args->fname != NULL) {
  170                 fname = imgp->args->fname;
  171                 sname = NULL;
  172         } else {
  173                 sname = sbuf_new_auto();
  174                 sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
  175                 sbuf_finish(sname);
  176                 fname = sbuf_data(sname);
  177         }
  178 
  179         /*
  180          * We need to "pop" (remove) the present value of arg[0], and "push"
  181          * either two or three new values in the arg[] list.  To do this,
  182          * we first shift all the other values in the `begin_argv' area to
  183          * provide the exact amount of room for the values added.  Set up
  184          * `offset' as the number of bytes to be added to the `begin_argv'
  185          * area, and 'length' as the number of bytes being removed.
  186          */
  187         offset = interpe - interpb + 1;                 /* interpreter */
  188         if (opte > optb)                                /* options (if any) */
  189                 offset += opte - optb + 1;
  190         offset += strlen(fname) + 1;                    /* fname of script */
  191         length = (imgp->args->argc == 0) ? 0 :
  192             strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
  193 
  194         if (offset - length > imgp->args->stringspace) {
  195                 if (sname != NULL)
  196                         sbuf_delete(sname);
  197                 return (E2BIG);
  198         }
  199 
  200         bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
  201             imgp->args->endp - (imgp->args->begin_argv + length));
  202 
  203         offset -= length;               /* calculate actual adjustment */
  204         imgp->args->begin_envv += offset;
  205         imgp->args->endp += offset;
  206         imgp->args->stringspace -= offset;
  207 
  208         /*
  209          * If there was no arg[0] when we started, then the interpreter_name
  210          * is adding an argument (instead of replacing the arg[0] we started
  211          * with).  And we're always adding an argument when we include the
  212          * full pathname of the original script.
  213          */
  214         if (imgp->args->argc == 0)
  215                 imgp->args->argc = 1;
  216         imgp->args->argc++;
  217 
  218         /*
  219          * The original arg[] list has been shifted appropriately.  Copy in
  220          * the interpreter name and options-string.
  221          */
  222         length = interpe - interpb;
  223         bcopy(interpb, imgp->args->buf, length);
  224         *(imgp->args->buf + length) = '\0';
  225         offset = length + 1;
  226         if (opte > optb) {
  227                 length = opte - optb;
  228                 bcopy(optb, imgp->args->buf + offset, length);
  229                 *(imgp->args->buf + offset + length) = '\0';
  230                 offset += length + 1;
  231                 imgp->args->argc++;
  232         }
  233 
  234         /*
  235          * Finally, add the filename onto the end for the interpreter to
  236          * use and copy the interpreter's name to imgp->interpreter_name
  237          * for exec to use.
  238          */
  239         error = copystr(fname, imgp->args->buf + offset, imgp->args->stringspace,
  240             &length);
  241 
  242         if (error == 0)
  243                 error = copystr(imgp->args->begin_argv, imgp->interpreter_name,
  244                     MAXSHELLCMDLEN, &length);
  245 
  246         if (sname != NULL)
  247                 sbuf_delete(sname);
  248         return (error);
  249 }
  250 
  251 /*
  252  * Tell kern_execve.c about it, with a little help from the linker.
  253  */
  254 static struct execsw shell_execsw = { exec_shell_imgact, "#!" };
  255 EXEC_SET(shell, shell_execsw);

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